The present embodiments relate to toner compositions for magnetic ink character recognition (“MICR”) and suitable for use in xerographic printing systems with offset lithographic print quality.
In the xerographic printing process, the image is generated after a series of steps which include charging of the surface of a photoreceptor, conversion of the computer data or original image into an optical or projected image, exposing the photoreceptor surface to the projected image, development of the toner particles on the photoreceptor by applying an electric field to the toner particles, transferring the toner particles from the photoreceptor to the media, and heating the toner particles so that they fuse together and permanently adhere to the media.
The magnetic toners used for printing may contain, for example, magnetic particles, such as magnetite in a fluid medium, and a magnetic coating of ferric oxide, chromium dioxide, or similar materials dispersed in a vehicle including binders and plasticizers.
Toners having magnetic ink character recognition (“MICR”) capabilities should contain magnetic particles having a high level of magnetic saturation (such as from 10 to 25). Magnetic saturation is the highest degree of magnetization that a material can achieve after exposure to a magnetic field. When characters printed using a toner having a sufficiently high magnetic saturation are exposed to a magnetic field prior to passing through the MICR scanner, the magnetic particles produce a measurable signal, also called waveform, that can vary in proportion to the amount of material deposited on the document being generated, the extent of magnetic saturation, and the sharpness of the MICR characters.
In order to compete effectively with offset printing, or for high quality color applications or for special effects, some xerographic devices add a fifth xerographic station to enable gamut extension via the addition of a fifth color. At any given time, the xerographic printing machine runs CMYK toners plus a fifth color in the fifth station, depending on the color space where the gamut extension is desired or a specific special effect. The area of gamut expansion depends on the color installed in the fifth station. A fifth color is any spot color or clear ink used in addition to the four color CMYK mix (Cyan, Magenta, Yellow and Black).
MICR toners can be more challenging to develop in some development subsystems. This is because the inclusion of the magnetite in the MICR toner makes the toner particle heavier and reduces the toner electrostatic charge as compared to the conventional toners. A heavier particle with lower electrostatic charge challenges Hybrid Scavengeless Development (“HSD”). This toner development method relies on powder cloud development. A powder cloud is formed between a toner donor roll and the surface of the photoreceptor due to an AC bias generated by a set of wires between the photoreceptor and the donor roll. In an HSD systems, all colors are developed to the photoreceptor via powder cloud, one color at a time, The charge of the toner particles and the electrostatic set points of the system are set so that not toner particles laying on the photoreceptor surface transfer back to a donor roll as the virtual image on the photoreceptor moves from one color station to another. Hence the term scavengeless development.
To increase the capability and applications of and HSD system with fifth station, there is a need to develop a fifth color toner having MICR capabilities to run in the fifth xerographic station.